1. Field of the Invention
The present invention relates to a semiconductor device having semiconductor chips bonded face down on a circuit-carrying substrate and to a manufacturing method thereof. More specifically, the present invention relates to a semiconductor device and manufacturing method having long-term reliability, improved heat radiation and increased packaging density all at the same time.
2. Discussion of the Related Art
One of the bonding methods used in the packaging of semiconductor chips is a face down bonding method. This is one of the so-called wireless bonding methods, in which, instead of using bonding wires, all circuit pads and bumps and beam leads that connect thereto are formed on an active surface, which is directly bonded face down to the conductor pattern on the circuit-carrying substrate.
One such face down bonding method is the flip chip bonding method for mounting semiconductor chips that use Cu balls or Sn--Pb solder bumps (e.g., ball grid array type devices). Bonding is carried out by pressing the bumps onto a corresponding conductor pattern on a temporarily soldered circuit-carrying substrate and hot depositing them. Since this method streamlines the assembly process, it is widely used for the packaging of hybrid ICs and for applications in main frame computers.
The flip-chip bonding method, in which the active surface faces downward, is effective for so-called bare chip packaging, which eliminates the use of packages and is aimed at achieving high-density packaging. In practice, this bonding method is often complemented by some kind of sealing procedure for enclosing or sealing the chip.
One widely known sealing procedure involves the use of a resin sealing layer for sealing the gap between the semiconductor chip and the substrate. However, the problem with the resin sealing layer is that the typical height of the bumps formed on the active surface of a semiconductor chip is only 50-100 .mu.m. In other words, the gap between the bonded semiconductor chip and the circuit-carrying substrate is very small. For this reason, it is difficult to fill the gap with resin even with a known method which uses a dispenser nozzle for discharging the resin.
Another type of sealing procedure involves the use of a cap, in which a cap made from an insulating material such as ceramics may be used to sealingly enclose the chip. The cap is placed on a circuit-carrying substrate and mounted so as to completely cover a semiconductor chip.
An example of such a cap is shown in FIG. 5. A semiconductor chip 13 is flip-chip bonded to a circuit-carrying substrate 11 having a printed circuit pattern 12. Semiconductor chip 13 is entirely contained within cap 15. The active surface 13a of the semiconductor chip 13 faces down, and circuit pads (not shown) exposed on the active surface 13a are connected to the print circuit pattern 12 via solder bumps 14. The cap 15 is fastened on the surface of the circuit-carrying substrate 11 via an insulting bonding material layer 16.
Although this configuration excels in airtightness, because the height of the cap 15 must be slightly higher than the height of the semiconductor chip 13 so as to avoid damaging the semiconductor chip 13, there is inevitably a small space left between the back surface 13b of the semiconductor chip 13 and the cap 15. The heat capacity of the air filling this space causes a lowering of the heat radiation effect. Moreover, since the cap 15 must be larger than the semiconductor chip 13, there is a limit to the extent that the packaging density can be increased.
As such, it has been very difficult to ensure long-term realizability, improve heat radiation and increase the packaging density using the conventional flip-chip bonding method. The object of this invention, therefore, is to provide a semiconductor device having a structure capable of satisfying all these demands simultaneously as well as to provide a method of manufacturing such a device.